1. Field of the Invention
This invention relates to chemical processes, and more particularly, to an efficient and inexpensive method for recovering uranium from process effluents, and the like.
2. Description of the Prior Art
In order to produce fuel for nuclear reactors, it is often necessary to convert uranium hexafluoride into uranium dioxide. A number of techniques have been developed for this purpose. It has been suggested, for example, to mix an aqueous solution of uranium hexafluoride with ammonia and carbon dioxide in the AUC process. In addition to a uranium precipitate, this process also produces a filtrate and an absorption washer waste that contain NH.sub.4 F (ammonium fluoride), ammonia and carbon dioxide as well as trace amounts of uranium. The carbon dioxide is removed from the filtrate through an expeller and thermosiphon evaporator loop, an expensive and complicated item of process equipment.
In subsequent stages, moreover, colloidal suspensions, or gels, are formed that liquify when stirred and solidify on standing. This characteristic, known as thixotropy, renders the fluoride precipitation and recovery stage inefficient, time-consuming and expensive.
There are further considerations that transcend the conventional chemical process economics. For instance, not only must the process wastes be environmentally acceptable but the uranium accumulated within the process stages also must at no time reach a "critical" mass sufficient to initiate an accidental nuclear fission reaction. In this latter regard, it has been noted that higher than usual concentrations of uranium in the filtrate that provides the feed for this process tends to cause an (NH.sub.4) .sub.3 UF.sub.8 precipitate in the first stage expeller.
It is possible that this precipitate might settle into a critical assembly that would produce a dangerous nuclear reaction.
Accordingly, there is a need for a safe, less expensive and more efficient uranium dioxide conversion waste treatment process than that which heretofore has been available.